Facile conversion of water to functional molecules and cross-linked polymeric films with efficient clusteroluminescence

Exploring approaches to utilize abundant water to synthesize functional molecules and polymers with efficient clusteroluminescence properties is highly significant but has yet to be reported. Herein, a chemistry of water and alkyne is developed. The synthesized products are proven as nonaromatic clusteroluminogens that could emit visible light. Their emission colors and luminescent efficiency could be adjusted by manipulating through-space interaction using different starting materials. Besides, the free-standing polymeric films with much high photoluminescence quantum yields (up to 45.7%) are in situ generated via a water-involved interfacial polymerization. The interfacial polymerization-enhanced emission of the polymeric films is observed, where the emission red-shifts and efficiency increases when the polymerization time is prolonged. The synthesized polymeric film is also verified as a Janus film. It exhibits a vapor-triggered reversible mechanical response which could be applied as a smart actuator. Thus, this work develops a method to synthesize clusteroluminogens using water, builds a clear structure-property relationship of clusteroluminogens, and provides a strategy to in situ construct functional water-based polymeric films.

-I found the extended discussion on how green water is (as a reagent) irrelevant to the current study, since DABCO is needed to promote the reaction. Likewise, I assume that the alkynes are not produced in a very "green" way.
-Abstract: "different water and alkyne" does not make sense to me. How can have different water? Do the authors mean "by reacting water with different alkynes".
-Title: The term "interfacial-polymers" is misleading/confusing to me. Do the authors mean polymers that are made using interfacial polymerization? If so, then perhaps the title should be updated as "...to Functional Cross-Linked Materials via Interfacial Polymerization with...". When I first read "interfacial polymers" I was not sure if the authors meant a linear polymer made by interfacial polymerization, such as nylon, or if they meant a block copolymer was being investigated, which can phase separate to yield heterogenous interfaces.
-Page 2, line 4: "Most species from water..." is an incomplete statement. Do the authors mean, most species prepared using water as a reactant..." -Page 2, line 8: replace "fluorine" by "fluorene" -Page 2, paragraph 3 (and elsewhere): I object to the term "artificial" to describe any chemical reaction that is not conducted biochemically. The root of this word, "artifice" means to deceive or trick. There is no trickery here, just a reaction that involves base-assisted addition of water to an alkyne.
-Page 5, lines 2-3: "...an intermolecular O---O distance of 2.883 Å in..."; see comment above. Moreover, all reported bond lengths and angles that are determined by X-ray crystallography should be given with their estimated standard deviations (esds).
-Much of the discussion related to how isotope substitution would influence the degree/strength of intermolecular interactions, such as hydrogen bonding, is not described well here. The authors are trying to rely on minor changes in emission data and XRD profiles to make fairly general statements. For example, I do not see how partial deuteration in a molecule would lead to difficulties in crystallization? Has this phenomenon been observed by others? There is a dearth of references to literature work in this section, to the point where it reads like "trust us" instead of a convincing argument for the role of isotopes in modifying the rigidity of a molecular framework in the solid state and thus its emission.
-Page 8, line 1: "significant [overlap] between pi and sigma electrons at LUMO" does not make any sense to be. A LUMO is an unoccupied orbital... Later the authors say "more considerable [overlap]", how was this judged? By eye? Or by measurable parameters? -Page 9: I am wondering why the authors did not use a diyne building block in their work? This should yield a soluble/processable linear polymer.
-Page 10, line 4: "the water concentration would be infinite". No. Pure water has a concentration of approximately 1000/18.01 M or 55.5 M under STP.
-Page 13: How heavy was the "drop ball"? -ESI: Table 1 requires R1, wR2 and GOF values for the X-ray data presented. Otherwise, it is difficult for others to determine the quality of the X-ray refinement procedures.
-ESI: How were the samples for the solid PL measurements prepared? Drop-cast from solution? etc..?
-ESI: Rf values should be given for all species purified by column chromatography.
- Fig S8 and S32: I am wondering why the authors did not use TD-DFT to probe the excitations leading to emission? Use of TD-FT is standard in the community these days.
-ESI: It is odd that "56 mg" of alkyne was used in each reaction? Was this on purpose or perhaps a copy/paste error?
Reviewer #2: Remarks to the Author: This manuscript describes the formation of clusteroluminescent compounds (CLgens) and polymers through a reaction of water molecules and alkynes in the presence of DABCO as an organic catalyst. Careful screening of the reaction using different types of water molecules such as heavy oxygen water (H<sub>2</sub><sup>18</sup>O) and heavy water (D<sub>2</sub>O) can suggest water involved reaction for the CLgen synthesis and the resulting molecular packing structures in their crystalline/solid-state control the through-space interactions (TSI). The small molecular CLgens' synthesis discussion is clear and well written. In this study, the CLgens' synthesis was applied at a water/organic solvent interface, and in the case of TMP as an alkyne reactant, the resulting product was 3D networking polymers. The new phenomenon of interfacial polymerization-induced emission (IPIE) sounds attractive. However, this reviewer claims the investigation of the polymer products. For the structure analysis, IR and <sup>13</sup>C CP/MAS were utilized. How about further analysis by means of XPS, elemental analysis, XRD, TGA, and DSC? There are discussions about crosslinking density of the polymeric films which depends on the polymerization time, however, no quantitative investigations such as porosity, surface area, density, etc, were carried out. Even AFM analysis, how are AFM images of 5 min and 20 min polymerization conditions? It may be possible to discuss more strictly the change of roughness evaluated from AFM. Is it really increasing the crosslinking (chemically) density or just aggregating the polymer and forming thicker films? In order to know this point, this reviewer recommends evaluating the polymer films by mechanical testing, such as a tensile test or bending test. Are they comparable to the 3D networking conventional polymers or elastomers? In the discussion about the actuator properties, I wonder about the responding speed and mechanical forces. Without such quantitative values, we are hard to imagine the performance and ability of the actuators. Overall, although this type of reaction is brand-new and attractive using water as a reactant to design nonaromatic fluorescent and vapor-responsive materials, I judge this study needs further investigation in particular the polymers produced at the water/organic solvent interface. Other minor suggestions are listed below. 2)"First" at the beginning of the Results is a typo.
3) It would be great if the authors study in-situ IPIE detection. How the emission change under growing the polymer film at the interface occur is interesting to know.

MS ID.:
NCOMMS-23-01434 MS Title: Facile conversion of water to functional molecules and cross-linked polymeric films with efficient clusteroluminescence

Response to the comments and suggestions of Reviewer 1
The reviewer commented that "The submitted communication by Tang and coworkers describes an interesting oligomerization/cross-linking reaction involving water as a building block. Running the reaction at a water/DCM solvent interface yields a cross-linked network material which has different morphologies on either side of the film, leading to a reversible film "curling" response in the presence of certain solvents. Likewise, emission enhancement is seen as the material becomes more cross-linked/rigid, in line with a type of aggregation-enhanced emission. Overall, this work reaches the level of novelty required for publication in Nature Comm., however, I have several major corrections that need to be addressed prior to publication." We sincerely thank the reviewer for the strong support of the main findings in this study and constructive suggestions that helped us to further the quality.
1. The reviewer commented that "The authors seem fond of using the term "polymerization-induced emission" or PIE to describe the luminescence in this work. However, the alkyne monomers themselves are weakly luminescent, so there is no "induction" of emission upon reaction with water, but an enhancement of emission.." Response: Thanks the reviewer for this comment. We have changed "interfacial polymerization-induced emission (IPIE)" to "interfacial polymerization-enhanced emission (IPEE)" as the reviewer suggested in the revised manuscript. Accordingly, we have added the above statement in the "Manipulation of TSI" section on page 8 of the revised manuscript.

The reviewer commented that "I found much of the initial work on the monomers and the explanation of subtle (reproducible?) differences in the emission a bit
cumbersome to read through. The authors should summarize the quantum yield, emission maxima, and lifetime data for each system in a  Figs. 39, 40). The results showed that no intermolecular OO interaction (e.g., O (lone pair) to O-E (E = element)) was observed. Instead, multiple hydrogen bonding interactions and n-pi interactions (C=O· · · C=C and O· · · C=C) were observed. These results verified that the intermolecular hydrogen bondings and n-pi interactions (C=O· · · C=C and O· · · C=C) played an essential role in the RIM mechanism and clusteroluminescence as the reviewer proposed. Therefore, we have deleted these intermolecular OO distances in Figs  Response: Thanks the reviewer for this suggestion. We have added more detailed information in the "Methods" section on pages 15 and 16 in the revised manuscript.
We also provide information on the fitting of lifetime data in Supplementary Figs. 41-47 and 57-59.
6. The reviewer commented that "The formation of the deuterated (D4) "dimers" outlined in Fig 4c is depicted in a misleading Fig. 22), D 4 isotopomers are the main products.
This reaction strictly requires a significant excess of water to obtain the products. According to the suggestion from the reviewer, we also conducted the reaction in a 1:2 D 2 O/alkyne ratio. However, no expected D 2 isotopomers could form.
7. The reviewer commented that "I found the extended discussion on how green water is (as a reagent) irrelevant to the current study, since DABCO is needed to promote the reaction. Likewise, I assume that the alkynes are not produced in a very "green" way." Response: Thanks the reviewer for this consideration. According to the suggestion, we just described these new H 2 O-involved reaction and interfacial polymerization and did not mention how green these reactions were in the revised manuscript. on page 2 of the revised manuscript.
11. The reviewer pointed out that "Page 2, line 8: replace "fluorine" by "fluorene"" Response: Thanks the reviewer for pointing it out. We have revised it on page 2 in our revised manuscript.

The reviewer commented that "Page 2, paragraph 3 (and elsewhere): I object to the term "artificial" to describe any chemical reaction that is not conducted
biochemically. The root of this word, "artifice" means to deceive or trick. There is no trickery here, just a reaction that involves base-assisted addition of water to an alkyne." Response: Thanks the reviewer for this suggestion. We have deleted "artificial" in the revised manuscript. Response: Thanks the reviewer for this comment. Here, we highlighted the intramolecular O· · · O interaction of EZ-DMODA with a distance of 2.883 Å, which was determined from the X-ray crystallography as shown in Fig. 2a. The electrostatic potential surface of EZ-DMODA also indicated such interaction with a negative potential region between these two oxygens atoms (Fig. 2c). However, no such an interaction was observed for its isomer of EE-DMODA. This interaction should be responsible for the red-shifted emission wavelength of EZ-DMODA compared with EE-DMODA. According to the suggestion from the reviewer, we have added all bond lengths and angles determined by X-ray crystallography with their estimated standard deviations in the "Additional Data" section in our revised Supplementary Information.
14. The reviewer commented that "Page 5, paragraph 1: "narrower energy gap"; "lower unoccupied molecular orbital (LUMO) [ Rev. 2021, 50, 12616-12655). It is also the reason why its electron delocalization cannot be observed from absorption spectra but appears in the excitation spectra. LUMO is occupied by excitons after photoexcitation. This overlap can obviously increase delocalization and narrow the energy gap, resulting in redshifted emission with a longer wavelength than the intrinsic conjugation level of molecular structure. Hence, the electron delocalization in the LUMO can provide the necessary information to explain such an unconventional luminescence. Based on the same calculation method and isovalue for orbitals, the electron overlaps of typical dimers of EE-OBBO and EE-DMODA could be observed by the naked eye (Fig. 6). EE-OBBO shows a greater number of overlaps (four for Dimer 5 and two for Dimer 6) than EE-DMODA (two for Dimer 1 and two for Dimer 2). Besides, the electron overlapping area of EE-OBBO is also larger than EE-DMODA. Moreover, the intermolecular distances in EE-OBBO are shorter than EE-DMODA as discussed in the manuscript. All of these parameters support that EE-OBBO showed stronger intermolecular TSI than EE-DMODA.
17. The reviewer commented that "Page 9: I am wondering why the authors did not use a diyne building block in their work? This should yield a soluble/processable linear polymer." Response: Thanks the reviewer for this consideration. We have tried to use a diyne building block to synthesize linear polymers. Interfacial polymerization cannot be used to synthesize linear polymers because the polymer film cannot be formed on the interface. However, when the polymerization was conducted in solution, only a tiny quantity of oligomers with very low molecular weights could be obtained. 19. The reviewer asked that "Page 13: How heavy was the "drop ball"?" Response: Thanks the reviewer for this question. Its weight is about 80 mg, and the weight of our soft mechanical arm is about 20 mg in Fig. 10c. We have added their weights in the caption of Fig. 10 that "Images of a soft mechanical arm (~ 20 mg) lifting a ball (~ 80 mg) upon exposure to DCM vapor and releasing it at 50 o C.".
20. The reviewer commented that "ESI: Table 1 requires R1, wR2 and GOF values for the X-ray data presented. Otherwise, it is difficult for others to determine the quality of the X-ray refinement procedures." Response: Thanks the reviewer for this comment. We have provided them in Supplementary Response: Thanks the reviewer for this comment. The samples prepared through recrystallization were used for solid PL measurements. Two pieces of quartz were utilized to hold the sample in the instrument, as shown in Fig. R1. 24. The reviewer commented that "ESI: It is odd that "56 mg" of alkyne was used in each reaction? Was this on purpose or perhaps a copy/paste error?" Response: Thanks the reviewer for this comment. "56 mg" is the weight of the organic catalyst DABCO.

Response to the comments and suggestions of Reviewer 2
The reviewer commented that "This manuscript describes the formation of clusteroluminescent compounds (CLgens) and polymers through a reaction of water molecules and alkynes in the presence of DABCO as an organic catalyst. Careful screening of the reaction using different types of water molecules such as heavy oxygen water (H 2 18 O) and heavy water (D 2 O) can suggest water involved reaction for the CLgen synthesis and the resulting molecular packing structures in their crystalline/solid-state control the through-space interactions (TSI). The small molecular CLgens' synthesis discussion is clear and well written. In this study, the CLgens' synthesis was applied at a water/organic solvent interface, and in the case of TMP as an alkyne reactant, the resulting product was 3D networking polymers. The new phenomenon of interfacial polymerization-induced emission (IPIE) sounds attractive.
Overall, although this type of reaction is brand-new and attractive using water as a reactant to design nonaromatic fluorescent and vapor-responsive materials, I judge this study needs further investigation in particular the polymers produced at the water/organic solvent interface. Other minor suggestions are listed below." We sincerely thank the reviewer for the strong support of the main findings in this study and constructive suggestions that helped us to further the quality.        For the density test, because it needs too many samples, we are so sorry that we could not do this test.
For AFM analysis, we tested AFM images of 5 min and 20 min polymerization conditions and did roughness analysis as the reviewer suggested. Root-mean-square roughness (R q ) and average roughness (R a ) are given by Nanoscope Analysis 1.8 ( Supplementary Figs. 60, 61 as shown below). When the polymerization time was prolonged, the R q and R a values decreased both on the water and DCM sides. It is also the evidence that tighter structures were formed and crosslinking density enhanced when the polymerization time was prolonged. We have added the roughness analysis on page 13 in the revised manuscript and Supplementary Information. For mechanical testing, the stress-strain curve for PTMP film (60 min) was obtained via TA Q800 dynamic thermal mechanical analyzer (DMA) ( Supplementary   Fig. 51). Its mechanical properties are comparable to reported crosslinked polymers obtained via the interfacial polymerizations (Angew. Chem. Int. Ed. 2022, e202117390). We have added the related descriptions on page 11 of the revised manuscript. The PTMP films at 5 min and 20 min polymerization times could not be tested because of many defects in their films.

5.
The reviewer pointed out that ""First" at the beginning of the Results is a typo." Response: Thanks the reviewer for pointing out that. We have revised it in the revised manuscript.
6. The reviewer commented that "It would be great if the authors study in-situ IPIE detection. How the emission change under growing the polymer film at the interface occur is interesting to know." were described separately. In addition, the heat capacity value for the glassy transition should be provided." Response: Thanks the reviewer for this comment. We described the DSC and PXRD results together as the reviewer suggested in the revised manuscript and provided the specific heat capacity difference (Δ Cp) in Supplementary Figure 49.